FIG. 1 shows an exemplary network structure of an Evolved Universal Mobile Telecommunications System (E-UMTS) as a mobile communication system to which a related art and the present invention are applied. The E-UMTS system is a system that has evolved from the existing UMTS system, and its standardization work is currently being performed by the 3GPP standards organization. The E-UMTS system can also be referred to as a LTE (Long-Term Evolution) system.
The E-UMTS network can roughly be divided into an E-UTRAN and a Core Network (CN). The E-UTRAN generally comprises a terminal (i.e., User Equipment (UE)), a base station (i.e., eNode B), an Access Gateway (AG) that is located at an end of the E-UMTS network and connects with one or more external networks. The AG may be divided into a part for processing user traffic and a part for handling control traffic. Here, an AG for processing new user traffic and an AG for processing control traffic can be communicated with each other by using a new interface. One eNode B may have one or more cells. An interface for transmitting the user traffic or the control traffic may be used among the eNode Bs. The CN may comprise an AG, nodes for user registration of other UEs, and the like. An interface may be used to distinguish the E-UTRAN and the CN from each other.
The various layers of the radio interface protocol between the mobile terminal and the network may be divided into a layer 1 (L1), a layer 2 (L2) and a layer 3 (L3), based upon the lower three layers of the Open System Interconnection (OSI) standard model that is well-known in the field of communications systems. Among these layers, Layer 1 (L1), namely, the physical layer, provides an information transfer service to an upper layer by using a physical channel, while a Radio Resource Control (RRC) layer located in the lowermost portion of the Layer 3 (L3) performs the function of controlling radio resources between the terminal and the network. To do so, the RRC layer exchanges RRC messages between the terminal and the network. The RRC layer may be located by being distributed in network nodes such as the eNode B, the AG, and the like, or may be located only in the eNode B or the AG.
FIG. 2 shows an exemplary control plane architecture of a radio interface protocol between a terminal and a UTRAN (UMTS Terrestrial Radio Access Network) according to the 3GPP radio access network standard. The radio interface protocol as shown in FIG. 2 is horizontally comprised of a physical layer, a data link layer, and a network layer, and vertically comprised of a user plane for transmitting user data and a control plane for transferring control signaling. The protocol layer in FIG. 2 may be divided into L1 (Layer 1), L2 (Layer 2), and L3 (Layer 3) based upon the lower three layers of the Open System Interconnection (OSI) standards model that is widely known in the field of communication systems.
The user plane (U-plane) denotes a path for transmitting data generated in the application layer, e.g., voice data, Internet Packet data, and the like. The control plane (C-plane) denotes a path for transmitting control messages used by the terminal and the network for a call management.
Hereinafter, particular layers of the radio protocol control plane of FIG. 2 and of the radio protocol user plane of FIG. 3 will be described below.
The physical layer (Layer 1) uses a physical channel to provide an information transfer service to a higher layer. The physical layer is connected with a medium access control (MAC) layer located thereabove via a transport channel, and data is transferred between the physical layer and the MAC layer via the transport channel. Also, between respectively different physical layers, namely, between the respective physical layers of the transmitting side (transmitter) and the receiving side (receiver), data is transferred via a physical channel.
The Medium Access Control (MAC) layer of Layer 2 provides services to a radio link control (RLC) layer (which is a higher layer) via a logical channel. The RLC layer of Layer 2 supports the transmission of data with reliability. It should be noted that if the RLC functions are implemented in and performed by the MAC layer, the RLC layer itself may not need to exist. The PDCP layer of Layer 2 performs a healer compression function that reduces unnecessary control information such that data being transmitted by employing Internet Protocol (IP) packets, such as IPv4 or IPv6 can be efficiently sent over a radio interface that has a relatively small bandwidth.
The Radio Resource Control (RRC) layer located at the lowermost portion of Layer 3 is only defined in the control plane, and handles the control of logical channels, transport channels, and physical channels with respect to the configuration, re-configuration and release of radio bearers (RB). Here, the RB refers to a service that is provided by Layer 2 for data transfer between the mobile terminal and the UTRAN.
As for channels used in downlink transmission for transmitting data from the network to the mobile terminal, there is a Broadcast Channel (BCH) used for transmitting system information, and a downlink Shared Channel (SCH) used for transmitting user traffic or control messages. A downlink multicast, traffic of broadcast service or control messages may be transmitted via the downlink SCH or via a separate downlink Multicast Channel (MCH). As for channels used in uplink transmission for transmitting data from the mobile terminal to the network, there is a Random Access Channel (RACH) used for transmitting an initial control message, and an uplink Shared Channel (SCH) used for transmitting user traffic or control messages.
Logical channels located above the transport channel and mapped onto the transport channel may include a Broadcast channel (BCCH), a Paging Control Channel (PCCH), a Common Control Channel (CCCH), a Multicast Control Channel (MCCH), a Multicast Traffic Channel (MTCH), and the like.
The physical channel is comprised of a plurality of sub-frames on a time axis and a plurality of sub-carriers on a frequency axis. Here, one sub-frame is comprised of a plurality of symbols on the time axis. One sub-frame is comprised of a plurality of resource blocks (RBs), and a resource block is comprised of a plurality of symbols and a plurality of sub-carriers. In addition, each sub-frame may use specific sub-carriers of specific symbols (e.g., a first symbol) of a corresponding sub-frame for the Physical Downlink Control Channel (PDCCH), that is, the L1/L2 control channel. One sub-frame has a time duration (or period) of 05 ms, and a Transmission Time Interval (TTI) indicating a unit of time that data is transmitted has a time duration of 1 ms, corresponding to 2 sub-frames.
As described above, the E-UTRAN is comprised of two parts: one is the base station and the other the terminal. Radio resources in one cell are comprised of uplink radio resources and downlink radio resources. The base station is configured to handle an allocation and a control of the uplink radio resources and the downlink radio resources of the cell. That is, the base station may determine when and which terminal uses which radio resources. For instance, the base station may determine to allocate a frequency in the range of 100 MHz and 101 MHz for a downlink data transmission in 3.2 seconds to a user 1 for 0.2 seconds. Then, the base station may inform this to the corresponding terminal such that the terminal may receive the downlink data. Similarly, the base station may determine when and which terminal uses which amount of radio resources for an uplink data transmission. Then, the base station may inform this to the corresponding terminal such that the terminal may perform the data transmission for the certain period of time. Contrary to the related art, dynamic management of the radio resources by the base station can be effective. The related art terminal is allowed to continue to use a radio resource as long as a call is connected. However, this would be unreasonable in consideration of a recent trend in which various services are based on the IP packet. This is because most of the packet services do not continuously generate a packet while the call is connected, resulting in many periods for not transmitting any data or packets. In this case, it would be very inefficient to continue to allocate radio resources to one terminal. In order to solve this problem, the E-UTRAN system has adopted the above-described allocation method for radio resources only if it is needed by the terminal and only when any service data is available.
Hereinafter, description of an RRC state of a terminal and a RRC connection method will be given in detail. The RRC state refers to whether the RRC of the terminal is logically connected to the RRC of the E-UTRAN, thereby forming a logical connection with the RRC of the E-UTRAN. If the RRC of the terminal forms a logical connection with the RRC of the E-UTRAN, this is referred to as an “RRC connected state.” Conversely, if there is no logical connection between the RRC of the terminal and the RRC of the E-UTRAN, this is referred to as an “RRC idle state.” When the terminal is in the RRC connected state and, accordingly, the E-UTRAN can recognize the existence of the corresponding terminal according to units of cells, the E-UTRAN can effectively control the terminal. On the other hand, the E-UTRAN cannot recognize a terminal that is in idle state. The terminal in idle state can be managed by the CN according to units of location areas or units of tracking areas, which are areas larger than the cell. Specifically, the existence of a terminal in idle state is only recognized according to units of large areas, such as location areas or tracking areas, and the terminal must transition into the connected state in order to receive typical mobile communication services such as voice or data.
When a user initially turns on the power of the terminal, the terminal first detects an appropriate cell and maintains its idle state in the corresponding cell. The terminal in idle state forms an RRC connection with the RRC of the E-UTRAN through the RRC connection procedure and transitions into the RRC connected state when the RRC connection needs to be formed. There are several instances in which a terminal in idle state is required to form the RRC connection. For example, an uplink data transmission may be required due to a call attempt by a user or the transmission of a response message in response to a paging message received from the E-UTRAN may be required.
Hereinafter, description of system information will be given. The system information may include all required information that a terminal should know for a connection with a base station. Accordingly, before the terminal attempts to connect to the base station, it should receive all system information and always have the most updated system information. In addition, considering that all terminals within one cell should know the system information, the base station periodically transmits the system information.
The system information may be divided into a Master Information Block (MIB), a Scheduling Block (SB), a System Information Block (SIB), and the like. The MIB serves to inform the terminal about a physical construction of a corresponding cell (e.g., a bandwidth, and the like). The SB serves to inform the terminal about transmission information of SIBs (e.g., a transmission period and the like). The SIB refers to a collection (aggregate) of system information that is related to each other. For instance, some SIBs may include information of neighboring cells only, and other SIBs may include information about an uplink radio channel only used by the terminal.